Using a process in FeCl2/NaOH or FeCl2 solution,the γ-Fe2O3,γ-Fe2O3/Ni2O3 nanoparticles were prepared from α-FeOOH,FeOOH/Mg (OH)2 and FeOOH/Ni(OH)2 precursor produced by precipitation.The precursor and as-prepared nanoparticles were characterized by vibrating sample magnetometer (VSM),X-ray diffraction (XRD),energy disperse X-ray spectroscopy (EDX),X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).A new transition induced chemically for preparing oxide nanoparticles is revealed.The as-prepared nanoparticles can adsorb FeCl3/FeCl2 to form an inert surface,which can help improve their chemical stability and prevent aggregation.The chemically induced transition in FeCl2 solution can be part of a new route for the preparation of single phase or composite oxide nanopartocles by the precipitation method.